Various resin paints have been developed and utilized as surface coating materials for motor vehicles and the like. However, these paints have merits and demerits and have poor general-purpose properties. Recently, however, a modified chlorinated polyolefin paint has been developed and utilized as a lacquer having excellent solvent resistance and general-purpose properties. As typical instances of the prior art, there can be mentioned Japanese Unexamined Patent Publication No. 58-176207 and Japanese Unexamined Patent Publication No. 60-1214. The latter Japanese Unexamined Patent Publication No. 60-1214 teaches that, in order to overcome defects of a chlorinated polyethylene paint and still retain excellent weatherability, chemical resistance, flame resistance, resistance against thermal aging, flexibility, sanitary characteristics, and electric characteristics, a modified chlorinated polyethylene formed by graft-polymerizing an unsaturated carboxylic acid or an anhydride thereof to chlorinated polyethylene is used. Chlorinated polyethylene per se has poor adhesion to metals and alloys such as iron, aluminum and steel, polar polymers and inorganic materials, such as mica and glass, but a modified chlorinated polyethylene formed by graft-polymerizing an unsaturated carboxylic acid to chlorinated polyethylene, has adhesion to these materials.
However, this modified chlorinated polyolefin paint is defective in that the storage stability of the lacquer is poor because the graft polymer is crystallized at low temperatures.
In this lacquer, the unsaturated carboxylic acid or its anhydride is left unreacted at the reaction step.
In practice, it is difficult to completely remove the residual unsaturated carboxylic acid or anhydride from the paint. The unreacted unsaturated carboxylic acid produces a smell at the coating operation, and this problem of smell generation is considered to be significant when carrying out the coating operation. The invention disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 60-1214 relates to a reaction process in which any remaining unreacted unsaturated carboxylic acid is controlled as much as possible. Nevertheless, even if this process is adopted, it is impossible to completely remove the odiferous unreacted unsaturated carboxylic acid from the coating composition.
Apart from this problem of odor, an improvement of the poor storage stability owing to crystallization of the graft polymer at low temperatures is not attained by either this prior invention or the invention of the above-mentioned Japanese Unexamined Patent Publication No. 58-176207.
Moreover, the coating compositions of these prior art techniques still have an unsatisfactory gasoline resistance, which is especially important for a primer for motor vehicles.